Uplink (UL) Coordinated Multiple Points (CoMP) has been accepted in 36.814 as an important candidate for enhancing UL capacity in an LTE-advanced system. For UL CoMP, more than one base stations (BSs) are configured to receive the UL transmission from a UE and the received signals are combined to get combining gain. The most important baseline for implementation of UL CoMP is that all involved base stations must be able to receive the UL transmissions from a UE, that is, the UE should perform UL synchronization with all involved base stations prior to the UL transmission so as to solve the different propagation delays between UE and involved base stations. For example, as shown in FIG. 6, this issue due to the difference between the propagation delays t1 and t2 for the involved base stations BS1 and BS2 must be resolved if UL CoMP is to be performed.
In general speaking. UL synchronization means that UE's transmission arrives at involved base stations within their Cyclic Prefix (CP)'s coverage; otherwise, if the UL transmission arrives at a base station before or late to its CP's coverage, the impacted base station may not decode this UL transmission correctly, hence the UL CoMP may not be achieved. In this case a feasible solution is provided to solve this problem. To guarantee UE's UL transmission arriving at the base station during its CP's coverage, a straightforward way is to design a longer CP to eliminate the impact of different propagation delays. As shown in FIG. 7, in FIG. 7, it is clear that the UL transmission to both BS1 and BS2 are in the CP's coverage. However, this solution has the following drawbacks:
1. It is very hard to determine an optimal CP length to cover different UL CoMP scenarios. For example, for scenarios where propagation delays to the involved base stations are similar, a small CP length is enough, however, it is not applicable to scenarios where the propagation delays varied dramatically. Also the longer CP will result in resource waste for scenarios with similar propagation delays.
2. This longer CP results in large overhead and leads to UL capacity loss. The reason is that the symbols which should be used to send data are now occupied by extended CP.
3. This solution may not support legacy UEs.
4. Scheduling flexibility is restricted since the UL CoMP may only be scheduled in the frame with longer CP length.